In the testing of integrated circuits, chips, and wafers, it is customary to use a system which includes a test head and equipment to handle the item to be tested. The handling equipment may be a packaged device handler, a wafer prober, or other apparatus. For simplicity, we will refer to such equipment as a “device handler” or simply “handler.” The test head is “docked” to the handler. Circuit connections can then be made between the test head and the integrated circuit so that the test head may perform the appropriate tests.
In general there are two methods of docking, actuator-driven docking and manipulator driven docking. The technique known as “actuator-driven” docking was first disclosed in U.S. Pat. No. 4,589,815 (hereinafter '815) due to Smith and variations on it were later developed and disclosed in U.S. Pat. No. 5,654,631 due to Ames, U.S. Pat. No. 5,744,974 due to Bogden, U.S. Pat. No. 5,982,182 due to Chiu et al, U.S. Pat. No. 6,104,202, due to Slocum et al, and U.S. Pat. No. 5,821,764 also due to Slocum et al. All are incorporated by reference.
In a general sense, docking systems require “alignment structures” on one of the two items to be docked that engage with “alignment receptacles” on the other of the two items. In the '815 patent, guide pins are included as the alignment structures, and guide pin receptacles and gussets are included as the alignment receptacles. In the three patents due to Chiu et al. and Slocum et al., alignment in all six degrees of freedom is provided by a kinematic coupling, which provides six contact points between provided surfaces where “no more than two of the contact points are colinear.” In these patents “kinematic surfaces” on one of the two items to be docked serve as alignment receptacles; and “kinematic mating surfaces” on the other of the two items function as alignment structures. In the preferred embodiments which are described in the patents, balls or spherical surfaces are the kinematic mating surfaces or alignment structures, and grooves are the kinematic surfaces or alignment receptacles. As is indicated in the patents, many other combinations of surfaces can be utilized.
The docking assembly described in the '815 patent is similar to the two-point docking assembly 1340 shown in part in the Vertical Plane Handler Position in FIG. 13 (and partially in cut away in the view in the lower left of FIG. 13) of the present application. In FIG. 13, only the half of the assembly that attaches to the test head is shown. These two-point docking assemblies both use two guide pins 912 and respective mating holes (not shown in FIG. 13) and two circular cams 910. When the cams 910 are rotated by handles 914 attached to them, the two halves of the dock are pulled together with the guide pins 912 becoming fully inserted into their mating holes (not shown). A wire cable 915 links the two cams 910 so that they rotate in synchronism. The cable arrangement enables the dock to be operated by applying force to just one or the other of the two handles 914. The handles are accordingly the docking actuator in this case.
Docks manufactured by Reid Ashman Manufacturing Company (RAM)[see web site and sales literature] are similar in concept to those described in the '815 patent. However, in the RAM dock linear cams are used instead of circular cams. Also the RAM dock uses rigid mechanical linkages and bell cranks instead of wire cables to synchronize the motion of the cams. The dock is actuated by one or the other of two handles that are coupled to respective bell cranks.
Powered actuators may be incorporated into docks in a variety of ways. For example a linear actuator, as previously described, may be readily added to impart docking actuation directly to the wire cable in the '815 dock or to the mechanical linkage or linear cams in other docks. The linear actuator may be any of several types including electrical motor powered, electrical solenoid, or pneumatic.
The docks described in U.S. Pat. Nos. 5,654,631 and 5,744,974 utilize guide pins and holes to align the two halves. However, the docks are actuated by vacuum devices which urge the two halves together when vacuum is applied. The two halves remain locked together so long as the vacuum is maintained.
The docks disclosed in U.S. Pat. Nos. 5,821,764, 5,982,182, and 6,104,202 use kinematic coupling techniques to provide the final alignment between the two halves. Guide pins may also be utilized to provide an initial alignment. The guide pins may be provided with a catch mechanism, which captures the guide pin in its hole and prevents it from escaping. The catch mechanism appears to activate automatically in the '764 and '202 patents; whereas, a motor driven device is utilized for each of the three guide pins in the '182 patent. Also in the '182 patent the three motors may be operated separately to effect planarization between the docked components. In all three disclosures a linear actuator is used to finally pull the two halves together. The linear actuator is disclosed as being of the pneumatic type.
The above discussion is intended to provide a brief overview of certain available actuator driven docking techniques. It is observed that the docks may be actuated by a variety of different devices.
An alternative approach, referred to a “manipulator-driven” docking, is described in, for example, U.S. Pat. Nos. 5,600,258 and 5,900,737 due to Graham et al. This alternative approach provides one or more powered and controlled axes (“controlled axes”) of the manipulator to position the test head. For example, and as described in the mentioned patents, the vertical, pitch, and roll axes are controlled axes in the Graham patents. Systems are also known where only a single axis, such as the vertical axis or tumble axis, is controlled. Position sensors, are typically used to provide feedback to the controlled axes concerning the position of the test head relative to the device handler/prober. In docking, a controller (or operator) operates the controlled axis or axes to first bring the test head into a ready to dock configuration and then continues to operate the controlled axes to complete the docking. In [Graham et al] the sensors are used by the controller to orient the docking surface of the test head properly with the docking surface of the device handler/prober (typically coplanar) and to stop motion when docking is complete and the electrical connections between the test head and the device handler/prober have been adequately made. There is no dock actuator and typically there is no separate, independent latching mechanism that is independent of the manipulator axes. If there is no separate, independent latch, the manipulator axes must be locked in position to maintain the test head in the fully docked position.
Also in manipulator-driven docking systems, it is not always desirable or feasible for the test head to be balanced in all axes. An unbalanced test head leads to unpredictable and unwanted forces that must be overcome by the drive and control mechanisms, by the alignment mechanisms, and by the structure of the device handler/prober itself.
A docking system in which a mechanism that is separate and independent of the manipulator latches the test head to the handler/prober when fully docked is referred to as a “latched docking” system. A system in which the test head is held in the fully docked position only by locking the manipulator axes is referred to as a “non-latched docking” system. Typically, an actuator-driven docking system is a latched docking system, and a manipulator-driven docking system is a non-latched docking system. However, the other two combinations are possible.
In the design of manipulators for large test heads, it is desirable to have the test head essentially freely movable in up to six axes or degrees of motion freedom to facilitate ease of controlled motion. This is true for manual manipulation and safe powering of motion axes as discussed in PCT international patent application No. US00/00704 “TEST HEAD MANIPULATOR” and in U.S. Provisional Patent Application No. 60/186,196 “COUNTER BALANCED VERTICAL DOCKING MOTION IN A DRIVEN VERTICAL AXIS TEST HEAD MANIPULATOR”. This is also true in docking/undocking with a device handler or prober, where motion is provided by a docking system as described in U.S. Pat. No. 4,589,815 due to Smith, U.S. Pat. Nos. 5,821,764 and 6,104,202 due to Slocum et al., or U.S. Pat. No. 5,982,182 due to Chin et al. Such freedom of motion or “compliant motion” is of particular importance in the process of docking the test head with the handler.
The two axes that provide motion parallel to the floor (side-to-side and in-out) and the axis that is perpendicular to the floor(up-down), are illustrated in FIG. 14. These three axes include the x-axis (side-to-side) 1315, the y-axis (in-out) 1325, and the z-axis (up-down) 1335. Also shown are three rotational axes including the pitch axis (x) 1310, the roll axis (y) 1320, and the swing (and yaw) axis (z) 1330. In the two axes that are parallel to the floor (x and y), motion freedom is normally provided by low friction bearings, rails, and the like or in an articulating arm as described in U.S. Pat. No. 4,527,942 also due to Smith. In the case of the vertical or up-down axis (z axis), it is typical to use counter weights to provide a substantially weightless condition to provide the desired freedom of motion at all times, except when an axis is deliberately locked by an operator. Other techniques in the up-down axis that are known are to use a spring mechanism as in U.S. Pat. No. 4,943,020 due to Beaucoup et al, pneumatic means such as in U.S. Pat. No. 5,931,048 due to Slocum et al., and U.S. Pat. Nos. 5,149,029 and 4,705,447 due to Smith. However, U.S. Pat. No 5,949,002 due to Alden points out certain difficulties with such approaches and proposes the use of a servo control loop incorporating a load cell force sensor. Techniques involving servo control loops with force and position feedback, however, are complex and expensive, and do not provide a simple way for an operator to override the system in case of a malfunction.
In the case of the pitch, roll, and yaw rotational motions, it is known to place the axes of rotations so that they pass nearly through the center of gravity of the test head and its attached mounting mechanisms and cables. This has been achieved in tumble mode manipulators by adding ballast counter-weights. On cable pivot manipulators, it has been achieved by providing a variety of spacers to vary the length of the inner cradle back on projected cable pivot manipulators as described in the U.S. Pat. No. 5,450,766 due to Holt.
It may be economical to place one or more of the rotational motion axis inside the test head at or near the actual center of gravity of the test head and cable assembly, as shown FIG. 13. Observe that pitch and yaw motions are integrated within the test head structure. In FIG. 13 these are shown as the pitch axis 1310(Theta X of ±5 degrees) and the yaw axis 1320(Theta Z of ±5 degrees). The roll axis 1330(Theta Y of ±90–95 degrees) is also shown in FIG. 13.
In contemporary systems, it may prove to be desirable to place the pitch axis with approximately ±5 degrees of motion, the roll axis with at least ±90 degrees of motion(external to the test head), and approximately ±5 degrees of yaw motion inside the test head. This is because the scope of the structure required to implement these axes at or near the center of gravity is significantly less than the structure required to implement these axes if they are external to the test head by, for example, using the “CPPJ” (for pitch) and the Split Ring Cable Pivot techniques described in U.S. Pat. No. 5,450,766 due to Holt and U.S. Pat. No. 5,608,333, also due to Holt, respectively.
It has been proposed to implement this concept by placing a spherical bearing near the center of gravity of a test head. An externally adjustable means of moving the position of the spherical bearing may be provided in the in-out direction so that it can be physically positioned to balance the pitch (or tumble) axis when the test head is in either the DUT(device under test) up or the DUT down orientation. A disadvantage of the spherical bearing is that it provides all three rotational degrees of motion simultaneously.
Although desirable, it is very difficult to place these internal axes at or very near to the true center of gravity of real test heads. The practice of varying the population of pin electronic boards inside of test heads and the size and weight of test head cables to satisfy specific tester end user's needs, often results in significant shifts in the location of the center of gravity and therefore significant imbalance forces. Additionally, as the test head is moved through its motion envelope, the forces exerted on the test head by the cable may vary; this causes a variable imbalance force as a system of fixed configuration is used. These imbalance forces impede the freely moveable state desired with respect to one or more of the axes of motion.
It is also frequently desirable to re-position the location of a motion axis to a location far from the center of gravity, whether the motion axis is internal in the test head or external to the test head as has traditionally been done on manipulators. An example of this is to position the tumble axis very near the DUT interface of a very thick test head rather than at the center of gravity of the test head which is usually near the physical center of the test head. If the test head is one meter thick, the implication of placing the tumble pivot axis at the center of gravity, therefore near the physical center, is that the manipulator would require a vertical motion range (stroke) of at least one meter(100 cm). If it is possible to place the tumble pivot axis within 13 cm of the DUT interface, the vertical stroke of the manipulator could be reduced by 74 cm (100 cm-26 cm″), thereby reducing the overall height of the manipulator or enabling longer main arms for greater load capacity from a given bearing structure. However, as indicated above, imbalance forces are created by moving the center of gravity of the test head away from a known physical point. Further, these imbalance forces cause the test head to be in an imbalanced state, such that it is not freely moveable in all six axes.
Accordingly, as test heads have become larger and more complex, there has been a corresponding increase in imbalance forces in each of the critical motion axes. It is desirable to have a means to allow these imbalances to be neutralized so that test heads may be manipulated and positioned effectively, while providing for the safety of both the operators and the equipment.